Carbon Dioxide Capture and Conversion to Organic Products

ABSTRACT

Methods and systems for capture of carbon dioxide and electrochemical conversion of the captured carbon dioxide to organic products are disclosed. A method may include, but is not limited to, steps (A) to (C). Step (A) may introduce a solvent to a first compartment of an electrochemical cell. Step (B) may capture carbon dioxide with at least one of guanidine, a guanidine derivative, pyrimidine, or a pyrimidine derivative to form a carbamic zwitterion. Step (C) may apply an electrical potential between an anode and a cathode sufficient for the cathode to reduce the carbamic zwitterion to a product mixture.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §120 of U.S.application Ser. No. 13/541,933 filed Jul. 5, 2012. The U.S. applicationSer. No. 13/541,933 filed Jul. 5, 2012 claims the benefit under 35U.S.C. §119(e) of U.S. Patent Application Ser. No. 61/504,828, filedJul. 6, 2011.

The above-listed applications are hereby incorporated by reference inits entirety.

FIELD

The present disclosure generally relates to the field of electrochemicalreactions, and more particularly to methods and/or systems for capturingcarbon dioxide and for electrochemical conversion of the captured carbondioxide to organic products.

BACKGROUND

The combustion of fossil fuels in activities such as electricitygeneration, transportation, and manufacturing produces billions of tonsof carbon dioxide annually. Research since the 1970s indicatesincreasing concentrations of carbon dioxide in the atmosphere may beresponsible for altering the Earth's climate, changing the pH of theocean and other potentially damaging effects. Countries around theworld, including the United States, are seeking ways to mitigateemissions of carbon dioxide.

A mechanism for mitigating emissions is to convert carbon dioxide intoeconomically valuable materials such as fuels and industrial chemicals.If the carbon dioxide is converted using energy from renewable sources,both mitigation of carbon dioxide emissions and conversion of renewableenergy into a chemical form that can be stored for later use may bepossible.

SUMMARY OF THE PREFERRED EMBODIMENTS

The present invention is directed to using particular capture agents,solvents, and/or electrolytes to capture/bind carbon dioxide and toreduce the captured carbon dioxide to organic products. The presentinvention includes the process, system, and various components thereof.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the disclosure as claimed. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate an embodiment of the disclosure andtogether with the general description, serve to explain the principlesof the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the present disclosure may be betterunderstood by those skilled in the art by reference to the accompanyingfigures in which:

FIG. 1A is a block diagram of a preferred system in accordance with anembodiment of the present disclosure;

FIG. 1B is a block diagram of a preferred system in accordance withanother embodiment of the present disclosure;

FIG. 2 is a flow diagram of a preferred method of capture of carbondioxide and electrochemical conversion of the carbon dioxide;

FIG. 3 is a flow diagram of another preferred method of capture ofcarbon dioxide and electrochemical conversion of the carbon dioxide; and

FIG. 4 is a flow diagram of a further preferred method of capture ofcarbon dioxide and electrochemical conversion of the carbon dioxide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the presently preferredembodiments of the present disclosure, examples of which are illustratedin the accompanying drawings.

In accordance with preferred embodiments of the present disclosure, anelectrochemical system is provided that captures carbon dioxide and thatconverts the captured carbon dioxide to organic products. Use of acarbon dioxide capture agent facilitates the capture process. Thecapture of carbon dioxide may refer herein to the binding of carbondioxide by reaction of carbon dioxide with a chemical to form anintermediate. It may also refer to the interaction between carbondioxide and a chemical to form an adduct. It may further refer to theinteraction between carbon dioxide and solvents into which the carbondioxide is bubbled, where the solvents may absorb carbon dioxide andhave enhanced solubility for carbon dioxide than does an aqueoussolution.

Before any embodiments of the invention are explained in detail, it isto be understood that the embodiments described below do not limit thescope of the claims that follow. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of termssuch as “including,” “comprising,” or “having” and variations thereofherein are generally meant to encompass the item listed thereafter andequivalents thereof as well as additional items. Further, unlessotherwise noted, technical terms may be used according to conventionalusage.

In certain preferred embodiments, the capture of carbon dioxide and thereduction of the captured carbon dioxide to produce organic products maybe preferably achieved in a divided electrochemical orphotoelectrochemical cell having at least two compartments. Onecompartment contains an anode suitable for oxidation, and anothercompartment contains a working cathode electrode and a carbon dioxidecapture agent. The compartments may be separated by a porous glass frit,microporous separator, ion exchange membrane, or other ion conductingbridge. Both compartments generally contain an aqueous or non-aqueoussolution of an electrolyte. Carbon dioxide gas may be continuouslybubbled through the cathodic electrolyte solution to preferably saturatethe solution or the solution may be pre-saturated with carbon dioxide.Mixing of carbon dioxide with the electrolyte solution and/or a carbondioxide capture agent may occur within the cathode chamber or in amixing chamber external to the cathode chamber.

Referring to FIG. 1A, a block diagram of a system 100 is shown inaccordance with an embodiment of the present invention. System 100 maybe utilized for capture of carbon dioxide and conversion of the capturedcarbon dioxide to organic products. The system (or apparatus) 100generally comprises a cell (or container) 102, a fluid source 104 (tosupply solvent to the cell 102), an energy source 106, a gas source 108,a product extractor 110 and an oxygen extractor 112. A product orproduct mixture may be output from the product extractor 110 afterextraction. An output gas containing oxygen may be output from theoxygen extractor 112 after extraction.

The cell 102 may be implemented as a divided cell. The divided cell maybe a divided electrochemical cell and/or a divided photochemical cell.The cell 102 is generally operational to capture carbon dioxide (CO₂)and to reduce carbon dioxide into products or product intermediates. Inparticular implementations, the cell 102 is operational to capturecarbon dioxide by binding carbon dioxide to a structure and/or moleculeand/or by increasing the solubility of carbon dioxide in the solvent.The reduction generally takes place by introducing (e.g., bubbling)carbon dioxide into an electrolyte solution in the cell 102. A carbondioxide capture agent in the cell may capture at least a portion of theintroduced carbon dioxide. In another implementation (as shown in FIG.1B), the carbon dioxide capture agent and the carbon dioxide interactexternal to the cathode chamber to permit capture of carbon dioxideprior to introduction to the cathode chamber. A cathode 120 in the cell102 may reduce the captured carbon dioxide into a product mixture, wherethe product mixture preferably includes organic products.

The cell 102 generally comprises two or more compartments (or chambers)114 a-114 b, a separator (or membrane) 116, an anode 118, and a cathode120. The anode 118 may be disposed in a given compartment (e.g., 114 a).The cathode 120 may be disposed in another compartment (e.g., 114 b) onan opposite side of the separator 116 as the anode 118. In particularimplementations, the cathode 120 includes materials suitable for thereduction of carbon dioxide including cadmium, a cadmium alloy, cobalt,a cobalt alloy, nickel, a nickel alloy, chromium, a chromium alloy,indium, an indium alloy, iron, an iron alloy, copper, a copper alloy,lead, a lead alloy, palladium, a palladium alloy, platinum, a platinumalloy, molybdenum, a molybdenum alloy, tungsten, a tungsten alloy,niobium, a niobium alloy, silver, a silver alloy, tin, a tin alloy,rhodium, a rhodium alloy, ruthenium, a ruthenium alloy, carbon, andmixtures thereof. An electrolyte solution 122 (e.g., anolyte orcatholyte 122) may fill both compartments 114 a-114 b. The electrolytesolution 122 may include water as a solvent with water soluble salts forproviding various cations and anions in solution, however an organicsolvent may also be utilized. A carbon dioxide capture agent 124 ispreferably added to the compartment 114 b, in certain implementations isalso added to the compartment 114 a, and in other implementations isadded to a mixing chamber 132 (as shown in FIG. 1B) external to thecompartment 114 b. For instance, the carbon dioxide capture agent 124may be utilized as the solvent and/or electrolyte for the compartments114 a and 114 b of the cell 102.

In a particular implementation, the carbon dioxide capture agent 124includes at least one of guanidine or a guanidine derivative. Carbondioxide capture agent 124 may include 1,1,3,3 tetramethylguanidine,1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene,and 1,4,5,6-tetrahydropyrimidine. In this implementation, the cell 102preferably includes an aqueous solvent, a solvent includingacetonitrile, dimethylfuran, or another organic solvent, or a mixture ofwater and an organic solvent (comprising between about 1% and 100% waterby volume). The carbon dioxide capture agent 124 may facilitate captureof carbon dioxide in the compartment 114 b (or in the mixing chamber132) by forming a carbamic zwitterion with the carbon dioxide. Uponapplication of an electric potential between the anode 118 and thecathode 120, the carbamic zwitterion is reduced at the cathode 120,generating an organic product and regenerating the carbon dioxidecapture agent. The organic product may include one or more ofacetaldehyde, acetate, acetic acid, acetone, 1-butanol, 2-butanol,2-butanone, carbon, carbon monoxide, carbonates, ethane, ethanol,ethylene, formaldehyde, formate, formic acid, glycolate, glycolic acid,glyoxal, glyoxylic acid, graphite, isopropanol, lactate, lactic acid,methane, methanol, oxalate, oxalic acid, propanal, 1-propanol, andpolymers containing carbon dioxide.

In another particular implementation, the carbon dioxide capture agentis an ionic liquid that includes at least one of a guanidinium-basedcation or a pyrimidium-based cation and preferably includes a halideanion, a sulfate anion, a phosphate anion, a nitrate anion, or anotheranion. The ionic liquid may act as a carbon dioxide capture 124 agent, asolvent, and an electrolyte. The ionic liquid may facilitate capture ofthe carbon dioxide (in the compartment 114 b or in the mixing chamber132) by increasing the solubility of the carbon dioxide as compared toan aqueous solvent. Upon application of an electric potential betweenthe anode 118 and the cathode 120, the captured carbon dioxide isreduced at the cathode 120, generating an organic product. The organicproduct may include one or more of acetaldehyde, acetate, acetic acid,acetone, 1-butanol, 2-butanol, 2-butanone, carbon, carbon monoxide,carbonates, ethane, ethanol, ethylene, formaldehyde, formate, formicacid, glycolate, glycolic acid, glyoxal, glyoxylic acid, graphite,isopropanol, lactate, lactic acid, methane, methanol, oxalate, oxalicacid, propanal, 1-propanol, and polymers containing carbon dioxide.

In another implementation, the carbon dioxide capture agent 124 includesa non-aqueous, organic solvent. The organic solvent preferably includesone or more of methanol, acetonitrile, and dimethylfuran, and mayinclude other organic solvents, provided that the organic solvent aidsin the capture of carbon dioxide, such by including a higher solubilitylimit for carbon dioxide as compared to an aqueous solvent. The captureof the carbon dioxide may occur in one or more of the compartment 114 band the mixing chamber 132. In this implementation, the cell 102 mayinclude an electrolyte suitable for a non-aqueous solvent, preferablywith a quaternary ammonium cation. The electrolyte may include ahalide-based anion. The compartment 114 b preferably includes apyridine-based catalyst to facilitate reduction of carbon dioxide at thecathode 120. Upon application of an electric potential between the anode118 and the cathode 120, the captured carbon dioxide is reduced at thecathode 120, generating an organic product. The organic product mayinclude one or more of carbon monoxide, carbonate, and oxalate.

The pH of the compartment 114 b is preferably between about 1 and 9. ApH range of between about 1 to about 4 is preferable for production ofcarboxylic acids from carbon dioxide. A pH range of between about 4 toabout 9 is preferable for production of other organic products (e.g.,carbonates, carboxylates, aldehydes, ketones, alcohols, alkanes, andalkenes) from carbon dioxide. Other pH values may be utilized, such aswhen the carbon dioxide capture agent 124 includes an ionic liquid or anorganic solvent.

The fluid source 104 preferably includes a water source, such that thefluid source 104 may provide pure water to the cell 102. The fluidsource 104 may provide other fluids to the cell 102, including anorganic solvent, such as methanol, acetonitrile, and dimethylfuran. Thefluid source 104 may also provide a mixture of an organic solvent andwater to the cell 102. In the implementations where the carbon dioxidecapture agent 124 is an ionic liquid, the fluid source 104 may providethe ionic liquid to the cell 102.

The energy source 106 may include a variable electrical power source.The energy source 106 may be operational to generate an electricalpotential between the anode 118 and the cathode 120. The electricalpotential may be a DC voltage. In preferred embodiments, the appliedelectrical potential is generally between about −0.5V vs. SCE and about−3V vs. SCE at the cathode, and preferably from about −0.6V vs. SCE toabout −2.5V vs. SCE at the cathode.

The gas source 108 preferably includes a carbon dioxide source. In someembodiments, carbon dioxide is bubbled directly into the compartment 114b containing the cathode 120. For instance, the compartment 114 b mayinclude a carbon dioxide input, such as a port 126 a configured to becoupled between the carbon dioxide source and the cathode 120. In otherpreferred embodiments, the carbon dioxide from the gas source 108 isintroduced to the mixing chamber 132, as shown in FIG. 1B. The carboncapture agent 124 may also be introduced to the mixing chamber 132. Themixing chamber 132 generally facilitates the interaction between thecarbon dioxide and the carbon capture agent 124 to permit the capture ofcarbon dioxide within the mixing chamber 132. In a particularimplementation, the mixing chamber 132 includes a stripping column tofacilitate interaction between the carbon dioxide and the carbon captureagent 124. The captured carbon dioxide may be introduced to the cathodecompartment 114 b for reduction of the captured carbon dioxide at thecathode 120 to produce a product mixture and to regenerate the carboncapture agent 124.

Advantageously, the carbon dioxide may be obtained from any source(e.g., an exhaust stream from fossil-fuel burning power or industrialplants, from geothermal or natural gas wells or the atmosphere itself).Most suitably, the carbon dioxide may be obtained from concentratedpoint sources of generation prior to being released into the atmosphere.For example, high concentration carbon dioxide sources may frequentlyaccompany natural gas in amounts of 5% to 50%, exist in flue gases offossil fuel (e.g., coal, natural gas, oil, etc.) burning power plants,and high purity carbon dioxide may be exhausted from cement factories,from fermenters used for industrial fermentation of ethanol, and fromthe manufacture of fertilizers and refined oil products. Certaingeothermal steams may also contain significant amounts of carbondioxide. The carbon dioxide emissions from varied industries, includinggeothermal wells, may be captured on-site. Thus, the capture and use ofexisting atmospheric carbon dioxide in accordance with some embodimentsof the present invention generally allow the carbon dioxide to be arenewable and essentially unlimited source of carbon.

The product extractor 110 may include an organic product and/orinorganic product extractor. The product extractor 110 generallyfacilitates extraction of one or more products from the electrolyte 122and/or the carbon dioxide capture agent 124. The extraction may occurvia one or more of a solid sorbent, carbon dioxide-assisted solidsorbent, liquid-liquid extraction, nanofiltration, and electrodialysis.The extracted products may be presented through a port 126 b of thesystem 100 for subsequent storage, consumption, and/or processing byother devices and/or processes. In particular implementations, theproduct is continuously removed from the cell 102, where cell 102operates on a continuous basis, such as through a continuous flow-singlepass reactor where fresh catholyte and carbon dioxide is fedcontinuously as the input, and where the output from the reactor iscontinuously removed. The carbon dioxide capture agent 124 may berecycled back into the compartment 114 b for capture of additionalcarbon dioxide.

The oxygen extractor 112 of FIG. 1 is generally operational to extractoxygen (e.g., O₂) byproducts created by the reduction of the carbondioxide and/or the oxidation of water. In preferred embodiments, theoxygen extractor 112 is a disengager/flash tank. The extracted oxygenmay be presented through a port 128 of the system 100 for subsequentstorage and/or consumption by other devices and/or processes. Chlorineand/or oxidatively evolved chemicals may also be byproducts in someconfigurations, such as in an embodiment of processes other than oxygenevolution occurring at the anode 118. Such processes may includechlorine evolution, oxidation of organics to other saleable products,waste water cleanup, and corrosion of a sacrificial anode. Any otherexcess gases (e.g., hydrogen) created by the reduction of the carbondioxide may be vented from the cell 102 via a port 130.

Referring to FIG. 2, a flow diagram of a preferred method 200 forcapture of carbon dioxide and electrochemical conversion of the carbondioxide is shown. The method (or process) 200 generally comprises a step(or block) 202, a step (or block) 204, and a step (or block) 206. Themethod 200 may be implemented using the system 100.

In the step 202, a solvent may be introduced to a first compartment ofan electrochemical cell. The first compartment may include an anode. Theelectrochemical cell may also include a second compartment containing acathode. Capturing carbon dioxide with at least one of guanidine, aguanidine derivative, pyrimidine, or a pyrimidine derivative may beperformed in the step 204. In the step 206, an electrical potential maybe applied between the anode and the cathode sufficient for the cathodeto reduce the carbamic zwitterion to a product mixture. The productmixture may include one or more of acetaldehyde, acetate, acetic acid,acetone, 1-butanol, 2-butanol, 2-butanone, carbon, carbon monoxide,carbonates, ethane, ethanol, ethylene, formaldehyde, formate, formicacid, glycolate, glycolic acid, glyoxal, glyoxylic acid, graphite,isopropanol, lactate, lactic acid, methane, methanol, oxalate, oxalicacid, propanal, 1-propanol, and polymers containing carbon dioxide.

Referring to FIG. 3, a flow diagram of another preferred method 300 forcapture of carbon dioxide and electrochemical conversion of the carbondioxide is shown. The method (or process) 300 generally comprises a step(or block) 302, a step (or block) 304, and a step (or block) 306. Themethod 300 may be implemented using the system 100.

In the step 302, an ionic liquid may be introduced to at least one of acathode compartment of an electrochemical cell or a mixing chamber. Theionic liquid may comprise at least one of a guanidinium-based cation ora pyrimidium-based cation. The electrochemical cell may include an anodein an anode compartment and may include a cathode in the cathodecompartment. Capturing carbon dioxide with the ionic liquid may beperformed in the step 304. The second compartment may include a cathode.In the step 306, an electrical potential may be applied between theanode and the cathode sufficient for the cathode to reduce the capturedcarbon dioxide to a product mixture. The product mixture may include oneor more of acetaldehyde, acetate, acetic acid, acetone, 1-butanol,2-butanol, 2-butanone, carbon, carbon monoxide, carbonates, ethane,ethanol, ethylene, formaldehyde, formate, formic acid, glycolate,glycolic acid, glyoxal, glyoxylic acid, graphite, isopropanol, lactate,lactic acid, methane, methanol, oxalate, oxalic acid, propanal,1-propanol, and polymers containing carbon dioxide.

Referring to FIG. 4, a flow diagram of another preferred method 400 forcapture of carbon dioxide and electrochemical conversion of the carbondioxide is shown. The method (or process) 400 generally comprises a step(or block) 402, a step (or block) 404, and a step (or block) 406. Themethod 400 may be implemented using the system 100.

In the step 402, a carbon dioxide capture agent may be introduced to atleast one of a cathode compartment of an electrochemical cell or amixing chamber. The carbon dioxide capture agent may comprise an organicsolvent. The electrochemical cell may include an anode in an anodecompartment and may include a cathode and a pyridine-based catalyst inthe cathode compartment. Capturing carbon dioxide with the carbondioxide capture agent may be performed in the step 404. The secondcompartment may include a cathode and a pyridine-based catalyst. In thestep 406, an electrical potential may be applied between the anode andthe cathode sufficient for the cathode to reduce the captured carbondioxide to a product mixture. The product mixture may include one ormore of carbon monoxide, carbonate, and oxalate.

It is believed that the present disclosure and many of its attendantadvantages will be understood by the foregoing description, and it willbe apparent that various changes may be made in the form, constructionand arrangement of the components thereof without departing from thescope and spirit of the disclosure or without sacrificing all of itsmaterial advantages. The form herein before described being merely anexplanatory embodiment thereof, it is the intention of the followingclaims to encompass and include such changes.

What is claimed is:
 1. A system for electrochemical reduction of carbon dioxide, comprising: an electrochemical cell including: a first cell compartment; an anode positioned within said first cell compartment; a second cell compartment; a cathode positioned within said second cell compartment, the second cell compartment including a carbamic zwitterion; and an energy source operably coupled with said anode and said cathode, said energy source configured to apply a voltage between said anode and said cathode to reduce the carbamic zwitterion at said cathode to a product mixture.
 2. The system of claim 1, wherein the carbamic zwitterion is formed in the second cell compartment by interacting carbon dioxide with at least one of guanidine or a guanidine derivative.
 3. The system of claim 1, wherein the carbamic zwitterion is formed in a mixing chamber by interacting carbon dioxide with at least one of guanidine or a guanidine derivative prior to introduction to said second cell compartment.
 4. The system of claim 1, wherein the energy source is further configured to apply a voltage between said anode and said cathode to regenerate a guanidine or a guanidine derivative.
 5. The system of claim 1, wherein the second compartment includes at least one of 1,1,3,3 tetramethylguanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, or 1,4,5,6-tetrahydropyrimidine. 